(i) Technical Field
The present invention relates to actuators.
(ii) Related Art
A step motor has a permanent magnet rotor and a coil. In order to improve efficiency, a stator is provided.
For example, Japanese Unexamined Patent Application Publication No. 2003-189584 discloses a step motor in which two pairs of plural coils and plural stators are arranged in the circumferential side of a permanent magnet rotor.
However, in the step motor acting as a conventional actuator, it is difficult to provide a uniform gap between the permanent magnet rotor and the stator. Also, the loss might be increased by the magnetic flux leakage and the conversion efficiency might be degraded. Further, a variation in driving speed might be generated.